PROJECT SUMMARY There is an urgent need for an efficient system to identify environmental factors that confer risk of autism spectrum disorder (ASD). Evidence indicates that ASD can arise from complex gene-environment interactions during critical periods of neurodevelopment. Genomic studies have identified hundreds of genes linked to ASD, many of which have well-characterized neurodevelopmental functions. However, the identification of non-heritable etiologic factors is lagging. The effort is complicated by the fact that candidate environmental factors must also be examined in combination with ASD-associated genetic variants to adequately assess adverse effects. We propose using Drosophila melanogaster as a model organism for the identification of environmental ASD-risk factors; the combination of rapid generation time, genetic tractability, and simple assays for investigating neurodevelopmental phenotypes makes Drosophila an ideal candidate. Moreover, many ASD-associated genes are functionally conserved in Drosophila, including the most common monogenic cause of ASD: fragile x mental retardation 1 (FMR1). This study will determine if developmental exposure to chemicals commonly used in the production of plastics?bisphenol-A (BPA), bisphenol-F (BPF), and bisphenol-S (BPS)?interfere with neurodevelopment in wild-type and fmr1 mutant Drosophila. BPA has established endocrine-disrupting capabilities, and recent studies indicate that BPA may also disrupt neurodevelopment. BPA-free plastics typically contain BPA-analogues, such as BPF or BPS, that have been linked to endocrine-disruption, but their role in neural development is largely unknown. Because of the ubiquity of plastics in our environment and ability of bisphenols to cross the placental and fetal blood-brain barriers, it is critical to determine the potential neurodevelopmental impacts of these pervasive environmental chemicals. In Aim 1, two courtship paradigms (including an associative learning paradigm) of Drosophila behavioral analysis will be used to delineate the relative neurodevelopmental impacts of BPA, BPF, and BPS on wild-type and fmr1 Drosophila. In Aim, 2 in vivo immunohistochemical methods will be used to determine if BPA, BPF, and BPS affect three neuronal phenotypes relevant to ASD and linked to fmr1 function?neural stem cell proliferation, axon outgrowth, and synapse formation. This study is significant because it will determine if bisphenols molecularly converge with fmr1 to affect specific ASD-associated phenotypes. More broadly, this project will help establish Drosophila as a model for the investigation of gene-environment interactions, which would provide a low-cost alternative to vertebrate models and accelerate the pace of in vivo toxicological assessment. This project closely aligns with the mission of the National Institute of Mental Health to identify etiologies of and preventative measures for mental illness; characterization of gene-environment interactions that confer risk of ASD is critical for establishing preventative measures and to better define the complex biological underpinnings of this increasingly prevalent disorder.